1. Field of the Invention
The present invention relates to a power unit for a vehicle in which the driving power is transmitted from an end portion of a crankshaft, via a primary reduction system and a clutch system, to a gear transmission housed in a crankcase of an engine. The invention particularly relates to an improvement on a twin-clutch transmission.
2. Description of Background Art
Japanese Patent Application Laid-Open Publication No. 2003-320861 discloses an example of power units for motorcycles in which a lever switching the clutch system between the engaged state and the disengaged state is placed outside of a clutch cover, which covers the clutch system.
The structure of a clutch system with a twin-clutch structure composed of a pair of hydraulic clutches requires an arrangement such that a relatively large part of the clutch system protrudes from a side of the crankcase along the axial direction of the crankshaft. When, as Japanese Patent Application Laid-Open Publication No. 2003-320861 discloses, the actuator switching the clutch system between engagement and disengagement is arranged further outside of the clutch system, the actuator, in such a structure, is arranged further outside of the clutch system that protrudes, to relatively large extent, from the crankcase. Such a structure leads, in the case of a motorcycle, to a smaller bank angle, and makes the space for the rider to rest his/her foot on hard to be obtained.
The present invention is made in view of the above-described problems. An object of the invention is to provide a clutch transmission in a power unit for vehicles with the following characteristics. While the clutch system has a twin-clutch structure, the power unit has as little protrusion toward the clutch system as possible.